Alloy steel and method of making



Nov. 25, 1958 c. G. MlcKELsoN ETAL 2,861,908

ALLOY STEEL AND METHOD 0E MAKING Filed Nov. 50, 1955 Nov. 25, 1958 c. G.MICKELSON ET AL 2,861,908

ALLOY STEEL AND METHOD oF MAKING 2 usw no" 8S a m M. 5 8 j@ Filed NOV.30, 1955 Nov. 25, 1958 c. G; MlcKELsoN ET AL 2,861,908

y ALLOY STEEL AND METHOD oF MAKING Filed Nov. 30, 1955 8 Sheets-Sheet 3RfzAr/a/vs/f/P afin/uw fmnmvsss No aw TEMPS/:Arana .muHA/sss )vo RAREEARTH Nov. 25, 1958 c. G. MlcKLsoN i-:TAL

ALLOY STEEL AND METHOD oF MAKING Filed Nov; so, 1955 8 Sheets-Sheet 4Nov. `25, 1958 c. G. MIcKELsoN i-:T AL 2,861,908

ALLOY STEEL AND METHOD OF MAKING Filed NOV. 50, 1955 8 Sheets-Sheet 5 BYecu'c @i m Nov. 25, 1958 c. G. MlcKl-:LsoN ET AL 2,861,908

ALLOY STEEL AND METHOD OF' MAKING Filed Nov. 30, 1955 8 Sheets-Sheet 6 uE lb U) 0 L z S u c lu E o "l 's u 'n 'n e E L n :a 2 g 'El v3 f g/MeeR/NELL HDNES# NUMBER HEAT No 777s /fNovEL mLoy HEAT No. 77/ No eoRo/vHEAT N0. 77/.9 No RA @E 5mm:

` zao Nov. 25, 1958 c. G. MICKELSON ET AL 2,861,908

ALLOY STEEL. AND METHOD oF MAKING 8 Sheets-Sheet 7 Filed Nov. 50, 195560 lloa .u m. MN w u wyfmn L D f c r P 6 l L u RN E ...0. M A 0 l L .n YR LCE 0 0 0 D Fm* m m. w w w m 600 800 TEMPERING TEMPERATURE 'E Nov. 25,1958 c.; G. MlcKELsoN ET AL 2,861,908 ALLOY STEEL AND METHOD OF' MAKINGI 8 Sheets-Sheet 8 Filed NOV. 50, 1955 7' ENS/LE YIELD BRINELL Euc WDM0F AREA CHARPY Evan/0N Patented Nov. 25, 1953 2,861,908 ALLY STEEL ANDMETHOD F MAKING Cedric G. Mickelson, Gary, Ind., and Gustaf A.Lillieqvist, deceased, late of Hammond, Ind., by Ellen S. Lillieqvist,administratrix, Lake County, Ind., assignors to American SteelFoundries, Chicago, Ill., a corporation of New Jersey AppiicationNovember 30, 1955, Serial No. 549,910 Claims. (Cl. 148-31) Thisapplication is a continuation-inpart of our copending application,Serial No. 451,- 652, led on August 23, 1954, nowv abandoned.

There has been a long felt need for a tough steel alloy having greatresistance to Wear without tendency to deform. For example, in theproduction of cast steel parts, such as clipper buckets or clipperteeth, which are subjected to frequent and severe abrasion as well asblows of substantial magnitude, Wear resistance and toughness, Withouttendency to deform, are of extreme importance.

Ordinary steels used in the production of such parts have not only beeninadequate to resist Wear but have in many cases tended to creep ordeform from repeated use, as is normally encountered in service.

hardened,

by a quench, is astonishinglytough and resistant to wear, Withouttendency to deform in service.

It has been found that the novel steel alloy after heat treatment ischaracterized by a tine grain microthe form of tough interlockedComponent Percent by Weight MM HRM Carbon about .20 to .50%.

Manganese. about .15 to 2.5%. Silicon about .1 to 2.0%. Phosphorus nilto about .05%.

Sulphur Molybdenum, Chromium, Tungsten (singly or in Combination).Nickel nil to about .07%. nil to about 5.0%.

nil to about 4.0%

Boron. about .0005 to .005% added to the metal state.

Rare Earth Metals in the molten The residue from the treatment of themolten metal in the molten state with about 0.0015 to 0.5%.

alance with residual impurities in ordinary amounts.

Iron B It has also been discovered that an economical composition of thenovel alloy limited to narrower ranges is particularly effective forcertain applications, in which case the following concentrations ofalloying elements Will produce an alloy having the desirablecharacteristic of wear resistance:

Component l Percent by Weight about .20 to .50%. about .70 to 1.70%.about .20 to 2.0%. nil tlo3 about .05%.

about .05 to .70%.

about 0.5 to 1.50%.

about .01 to 1.00%.

about .0005 to .0057 added to the metal in the molten state.

The residue from the treatment of the molten metal in the molten statewith about 0.0015 to 0.5

B ance with residual impurities in ordinary amoun It may also be notedthat titanium in an amount of the order of nil to 5 pounds per ton ofcharge may be added to the alloy in the molten state prior to additionof the boron and rare earths; Titanium is preferably added in the formof ferrotitanium although other forms thereof may be used. Under certainmelting conditions it has been found that the addition of'titanium iscritical as, for example, when the steel is cast .at a very hightemperature or has been subjected to a long hold after having beenkilled in the furnace. Under these conditions nitrogen absorption by thesteel may be very high. Also a heat having a poor boil may tend to havea high soluble vnitrogen content. Under any one of these conditionstltanium must be added to change the soluble mtrogen to the extent thatthe titanium combines with soluble nitrogen. The effective range oftitanium for the purpose is from about .0005 to about .02% by weight.

It has been found that a low carbo-n alloy steel such as above describedhaving the desired characteristic of Wear resistance and presentingminimum diculties from centrations of alloying elements:

Percent by Weight about .26 to .30%.

about 1.35 to about 1.55%. about .30 to .46%.

Component Carbon A higher carbon alloy having even'greater resistance towear, but presenting certain difficulties from a viewpoint of the heattreatment, has been foundrto contain the following concentrations ofalloying elements:

Percent by Weight about .33 to .37%. about 1.35 to 1.55%. about .30 to.46%. nil to about .020%

Do, about .47 to .53%. about .52 to .68%. residual Component Nickel RareEarth Metals The residue from the treatment of the molten metal in themolten state with about 0.0015 to 0.5%. Boron... about .0020 to .005%added to the metal in the molten state. l Balance with residualimpurities in ordinary amounts.

Iron

According to the invention, the novel steel alloy, after castingthereof, is heat treated in the following manner to achieve maximum wearresistance and toughness. The castings are first normalized by heatingthem, for example, to about 1600-1900" F. After a hold of any desiredduration, the castings are then air cooled so that they may beconveniently worked in lthe shop. This treatment is followed by ahardening heat treatment in which the castings formed of the lowercarbon steel alloy above mentioned are heated, for example, to about1500# 1700" F., and the higher carbon alloy steel castings are heated,for example, to about 1450-1650" F. ln either case the castings arepreferably held at the hardening temperature for about an hour or more,depending upon the section and are then quenched, preferably in water.

The castings are then heated to a tempering ternperature of the order of100 F. or more up to but less than 600 F., although unusually excellentresults have been attained within `a range of about 250 to 450 F. Thecastings are held at the tempering temperature, preferably for a periodof about two hours or more depending upon the size of the castings andare then quenched, preferably in water, or possibly inair.

It will be understood that the hold time for the various heat treatmentsmay vary considerably depending v upon the type of furnace equipment andthe size of material being produced. The shortest possible time attemperature is preferred, and it may be noted that excellent resultshave been achieved by the foregoing practice. If desired, in addition tothe above described heat treatment, the castings may be tempered beforehardenlng to reduce machining costs.

rare earth elements are then added,

The term rare earth metals as used herein is intended to mean thefollowing elements either singly or in combination: cerium, lanthanum,neodymium, praseodymium, samarium, illinium, europium, gadolinium,dysprosium, ytterbium, their alloys and compounds.

These rare earth metals may be in the form of a mixture commonly knownas misch metal. A mixture of rare earth metals which has provedparticularly effective contains about 31.5% lanthanum, about 44.5%ceriurn, about 11% praseodymium, about 7% neodymium and about 6% of theother rare earth metals above mentioned.

The percentage of rare earth metals and boron additions is critical andmust be maintained substantially within the ranges set out above.

It is also noted that the tempering temperature is critical inasmuch asit has been discovered that brittleness of the castings is caused bytempering at a temperature of about 700 F., and wear resistance of thecastings is inadequate if they are tempered at a temperature in excessof 700 F. Under certain conditions, the tempering step may be eliminatedentirely, although this is not ordinarily desirable.

It has been found that in manufacturing the steel alloy of thisinvention, the molten steel is preferably killed in the furnace as, forexample, by adding a deoxidizer such as aluminum, ferromanganese,ferrochrome, silicomanganese and/ or ferrosil-icon. When the ladle ispartly full, the steel is preferably further deoxidized, and thenaluminum and titanium (if any) are preferably added, the aluminum beingin an amount of the order of The boron and irrespective of sequence; andfinally an addition of calcium silicon is made, preferably in an amountof the order of three pounds per ton of charge before the ladle iscompletely lled.

If the steel is produced in small quantities, as, for example, in aninduction furnace, the additions may be made in the furnace prior topouring of the heat.

It has been further discovered that, within the ranges above specified,the alloying elements are effective only if the addition is made tomolten steel in a basic condition, and it may be noted that the alloyingelements may be added to the ladle as the basic steel is poured from thefurnace; or if an acid lined furnace is used, the molten steel and slagmay be poured into a first ladle wherein the slag may be converted to abasic condition, and the steel and slag may then be poured into a secondladle wherein the alloying additions are made.

The unusual properties of steel castings produced in the foregoingmanner are best demonstrated by referring to tests of castings whichwere composed and heat treated within the specified ranges. The resultsof these tests are set forth in the tables which appear hereafter and inthe accompanying drawings, wherein:

Figure 1 lis a graph illustrating the eiect of tempering temperatures onthe toughness of the novel steel alloy casting (about .25% carbon) atroom temperature;

Figure 2 is a graph illustrating the effect of tempering temperatures onthe toughness of the same steel alloy one to five pounds per ton ofcharge.

Vcastings at low temperatures of the-order of 40 F.;

Yorder of 1000" F. or more;

Figure 7 is a graph comparing the toughness of the 'i Y' novel steelalloy castings (about .26% carbon) with those of substantially identicalsteel castings produced and heat Block No. (ontreated in the same mannerbut lacking either boron or Vrrtilello rare earth metals;

Figure 8 is a graph showing the effect of tempering 7816 47 5 48 47 47u5472 temperatures on the physlcalcharacteristics of the novel 7815lgng-g. eel alloy castings containing about .30% carbon; ggg 47;?7h48-5jjjjjjjjj 472 Figure 9 is a graph showing the effect of tempering7816 temperatures on the physical characteristics of the novel steelalloy castings containing about .25% carbon and about 1.0% -chromium andnickel.

Specific examples are disclosed as follows:

Example No. 1

Two heats were poured with the following analyses:

Heat No. C Mn Si P S Cr Mo Ni B Heat No. 7816 of the molten steel waskilled in a basic lined induction furnace by adding 11/2 pounds ofaluminum per ton of charge, then .0024% boron, then 2 pounds of theabove descr' 19-18-18-19-.. 18. f 472 per ton of c l1a1ge, and 22 21 2121 21o 46:5 manganese-slllcon per ton of charge. The boron was ggg ggg251m 713 added in the form of a composition known as Borosil 816 411 2120 22*22I 21 458 95 7 whlch` 1s a mixture made up prlmarily of about 3%ggg 5 1820*19 19- jf boron, about silicon, and the remainder iron, al-781s 7 17.5 415 though other types of boron containing materials may7816 23`22`2321- 22 385 781s 32-26-32-32 30.5 se be used 1f deslred.7816 40-40-39-30 39.5 838 The molten steel of HeatNo. 7817 was killed ina ggg 5 basic lined induction furnace by adding 21/2 pounds of 40 781513 59 222 aluminum per ton of charge, then .0024% boron, added im 5 ggas BorosiL and nally 3 pounds of calcium-manganese- 7817 2,- 16 45s fsrllcon per t0n of charge. ggg 4- 215 Both heats were poured intostandard block test run- 7817 5 18.5 1go ners which were normalized andcut into sections 21/2 gg; s g1g g inches long. 7817 8--- 16.5 880 Allsections were normalized by heating to 1750 F., ggg lo g' at whichtemperature value the sections were held for 7817 11 39 2 78 two hours.The sections were then air cooled and were ggg gli: hardened by heatingto 1650 P., at which temperature value the sections were held for onehour followed by a Charpy results at *40 F. were as follows; waterquench. The tempering heat treatment tor these y sections was asfollows: Blnell Average R(F om oe. yel HCH) 7815 AQ 1.8 472 Heat andBlock No. Temperature, Hold, Cooling 7816/7817 AQ F. hrs. 7816 3 22.5472 m M 7815 4 21 458 100 2 Water quench. 20o 2 Do. t 300 2 D0 7816 714.5 415 400 2 DO- 7816 8 18.5 385 500 2 DO- 7810 9.- 19.5 855 600 2 Do-7816 10 26.5 838 700 2 DO- 7815 11- 51.5 282 200 2 Do- 65 7816 12 08.524.4 900 2 Do. 5 1, 000 2 Do. 15' 4.58 1,100 2 Do. 15 4:8 1, 200 2 Do.l@ 5 s 11300 2 D0' 7817 15. 5 152 7817 12 440 7817 11 421 7817 12 4057817 11.5 380 7817 1s 851 After heat treatment the sections weremachined into gg; 34-37 3S 5 ggg four Charpy specimens. Hardnessreadings taken on 7817 12- 40-34 36-88 55.5 238 the tested Charpyspecimens were as follows: 7817 13' 29`22`3Fr35 30' 220 The graphs shownin Figures 1-4 were derived from the foregoing data and illustraterelationships found to exist with respect to tempering temperatures,toughness, hardness and addition practice.

Referring to Figure 1, it will be seen that a brittle zone resulted froma tempering temperature of the order of 700 F., in the case of the novelsteel alloy containing rare earth elements and boron (Heat No. 7816) asillustrated by the top line in this graph. The sections heat treated attemperature values above 700 F. were found to have inadequate resistanceto wear due to the low hardness values shown in Figure 4. Referringagain to Figure l, it will be seen that the best results with respect totoughness were achieved by tempering temperatures between 300 and 400FL, although very good results in this regard were attained by temperingtemperatures below 600 F.

Referring to Figure 2, it will be seen that a low temperature brittlezone resulted from a tempering .temperature of 700 F. in the case of thenovel steel alloy containing rare earth elements and boron (Heat No.7816) illustrated by the upper line of the graph. The best results inthis regard resulted from tempering temperatures between 3,00 and 400F., although good results were attained at temperatures below 600 F.

As illustrated by both graphs of Figures 1 and 2, the novel steel alloy(Heat No. 7816) Was greatly superior from a viewpoint of toughness thanthat to which the rare earth elements were not added (Heat No. 7817).

Referring now to Figure 3, it will be seen that a brittle zone wasdiscovered in the novel steel alloy (Heat No. 7816) at a Brinellhardness of approximately 415. At greater hardness values than 415,toughness increased, with the best results from this viewpoint at aBrinell hardness of 440 or greater.

Referring now to Figures 5 and 6, it will be seen that Figure 5illustrates the microstructure of a casting composed of the novel steelalloy magnified 600 times. The steel alloy casting of Figure 5 iscomposed of Heat No. 7816 normalized and hardened as above described,and tempered at 375 F. It will be noted, as seen in Figure 5, that themicrostructure is fine, predominately in the form of tough interlockedmartensitic needles. 'Ihe steel alloy casting shown in Figure 6 is alsomagnified 600 times7 and it will be seen that the martensitic needlesare no longer plainly visible in the microstructure of Figure 6 due tothe fact that this casting was tempered at about l000 F. or more. As aresult the wear resistance of the steel alloy casting shown in Figure 6is quite inferior to that of Figure 5.

Example No. 2

Heat No. 7773 was' treated in the molten state in accordance with theabove described practice with 11/2 pounds `of aluminum per ton ofcharge, then 2 pounds of the rare earth metal mixture per t0n of charge,then .002.4% boron added in the form of Borosil, and

finally 3 pounds of calcium-manganese-silicon per ton of charge.

Heat No. 7719 was treated in the molten state by adding 21/2 pounds ofaluminum per ton of charge, then .0024% boron addedA as BorosiL andfinally 3 pounds of calcium-manganese-silicon per ton of charge.

Heat No. 7718 was treated in the molten state by adding 11/2 pounds ofaluminum per ton of charge, then 2 pounds of the rare earth metalmixture per ton of charge, and finally 3 pounds ofcalcium-manganese-silicon per ton of charge.

All three of these vheats were produced in basic lined inductionfurnaces, and the addition practice was identical except for the factthat the rare earth metal mixture was eliminated from Heat No. 7719 andboron was eliminated from Heat No. 7718.

Steel from these heats1was poured into test runners from ll x 6" x 10Charpy blocks. All runners and the Charpy blocks were normalized at 1750F. for 2 hours. The runners were machined into plugs and inserted into5" Charpy blocks. All blocks were then hardened by .heating to 1650u F.,holding one hour and water quench- Heat and Block No. Tempera- Hold,Cooling ture, F. hours 7773-10, 7719-IC 7718-IC 1,000 2 water quench.7773-IX, 7719-Dix, 7718-1X 1, 050 2 Do. 7773-IA, 7719IA, 7718-IA.. 1, 2D0. 7773-20, 7719-20, 7718- 1, 100 2 D0. 7773-2X, 7719-2X, 77l8-2X l,165 2 Do. 7773-2A, 7719-2A, 7718-2A 1, 210 2 D0. 7773-50, 7719-5C7718-5C. 1, 120 2 Do. 7773-5X, 7719-5x, 7718-5X 1,185 2 D0. 7773-5A,7719-5A, 7718-5A-. 1, 250 2 D0. 7773-8() 1, 120 2 D0. 7 773-8X- 1, 185 2D0. 7 773-8A.. 1, 250 2 Do. 7719-8C-- 1,120v 2 Do. 7719-8 1,185 2 Do.

After iinal heat taken from slices of Heat and Rockwell C ReadingsCenter to Surface Block No.

Charpy specimens were machined from the plugs and fromV the 5 inchCharpy blocks, and the results when tested at 40 F. were as follows:

Heat and Location of Notch Foot Pounds Avg. Average Block No. -40 F.Brinell 7773-5C l from surface 50-51-5454 from s11rfaee g--ii 53'4 287rom sur ace 6 -60-65- l g4 g2gg4 6 62.9 261 9- y 7-7 7719-5o i inzqig70.3 241 i2%ffromsurrace.... 3s-4o-4339 i 38'5 279 7719-5X 1" fromsurface 37-40-40-40 41 2 25S 2% from surace 43-43-43-43 7719-5A {V' fromsurface 44-444345 44 0 23S 2% from surfaee. 44--44-45-44 7718-5C {V fromsurface... 22-23-23-25 20 0 272 2%" from surface 18-19-16-14 7718-5X {1from surface. 36-38--40-33 l 33 2 2K5 2% from surfe 30-33-28-27 l7718-5A l1 from surface 39-48-49-44 42 6 229 2% from surfaee 37-42-41-41Example No. 3

A basic lined inductionr furnace heat was produced in accordance withthe following table:

1650 F. followed by a water quench after one hour hold at temperatureand were then tempered for two hours by heating to various temperaturesfollowed by a water quench. The tempering temperatures used werevselected to give a hard ess range from 250 to 500 Brinell in incrementsof approximately 50 points Brinell. All pull bar specimens were aged for24 hours at 250 F. Th following table lists the mechanical properties ofboron in the form of that tests at 40 F. disclosed a brittle zone forthe samples tempered at 700 F., and the samples'V tempered at 550 F. orless were much tougher atV -40 F. than those tempered at temperaturesbetween 600 and 800 F. Furthermore the Brinell hardness of samplestempered above 700 F. indicate unsatisfactory resistance to wear'.

Example N0. 4 A 200 pound basic induction furnace heatof the novel 10steel alloy having the composition shown inl the following table wasproduced in the usual manner:

The heat was deoXidized by adding 11/2 pounds of aluminum per ton.Following the deoxidization, 2 pounds of the rare earth metal mixtureper ton and .0027% Borosil were added. Finally 3 pounds ofcalcium-manganese-silicon per ton were added.

Runners cast from this heat were normalized by heating to 1750 F. Afteratwo hour hold at temperature, the runners were softened at 1250 F. fortwo hours and were then air cooled. The runners were then water quenchedfrom 1650or F. after a one hour hold at temperature aridwere thentempered by holding for two hours at various temperatures followed by awater quench. The` tempering temperatures used were selected to givecastings obtained from this heat: hardness range from approx1mately 250to 450 Brinell Charpy Impact, Heat Tempering Yield Tensile Elonga- Red.of Ft. Lbs. N o. Serial N o. Tempera- Strength Strength tion, Per- Area,Per- BHN ture, F. (p. s. i.) (p. s. i.) cent cent Rm. T. F.

1 250 198, 750 24S, 500 10. 0 31. 5 18-17 13-16 514 2 250 219, 000 246,000 9. 5 29. 8 17-17 15-15 514 Average 250 208, 875 247, 250 9 75 30. 717. 25 14. 75 514 3 350 195, 000 239, 500 9. 5 31. 2 17-16 16-17 495 4350 195, 000 235, 500 9. 0 30. 2 18-19 16-16 495 Average 350 195,000237, 500 9. 25 30. 7 17. 25 16. 25 495 5 550 195, 000 224, 000 9. 5 31.8 12-13 13-9 444 6 550 195, 000 224, 500 10. O 29. 8 11-12 13-13 444Average 550 195, 000 224, 250 9. 75 30. 8 12. 00 l2. 00 444 l 7 750 188,000 204, 500 11.0 33. 8 14-14 10-10 429 9203 8 750 189, 000 204, 500 10.`5 33. 8 15-13 7-10 429 Average 750 188, 500 204, 500 10. 75 33. 8 14.00 9. 25 429 9 950 164, 000 177, 500 13. O 37. 0 26-26 16-17 388 l0 950167, 500 178, 00D 13. 0 35. 7 26-27 16-16 375 Average 950 165, 750 177,750 13. 0 36. 4 26. 25 16. 25 382 11 1, 050 1,50, 000 161, 500 15. O 44.9 35-35 30-31 352 12 1, 050 149, 500 161., 500 15. 5 47. 5 36-36 29-27352 Average l, O 149, 750 161, 500 15. 3 46. 2 35. 50 29. 25 352 13 1,250 99, 000 117, 000 2l. 0 58. l 63-65 57-59 248 14 1, 250 100, 000 119,G00 21. 5 57. 0 6965 65H36 255 Average 1, 250 99, 500 118, 000 21. 3 57.6 65. 50 61. 75 252 The data of the foregoing table in connection withHeat No.` 9203 is presented graphically in Figure 8, which emphasizesthe effect of tempering temperature on the mechanical properties of thesteel alloy. lt may be noted Temperng Temperature, F.

Serial No.

4 Average 1 5 800 Averag; 800

8 Average 9 10 Average l l 12 Average 1, 250 95,-500 115, 250 76. 8 71.8

1 Detective bar. Not included in average data for Figure 9.

ing table lists the mechanical properties obtained from this heat:

Charpy Im pact, Yield Tensile Elonga- Red. of Ft. Lbs. Strength Strengthtion, Per- Area, Per- (p. s. i.) (p. s. i.) cent cent Rm. T 40 F 181,500 228, 000 9.0 32. l 27-22 23-20 183, 000 230, 500 9. 0 33. 4 24-2422-25 182, 250 229, 250 9. 0 32. 8 24. 3 22. 5 No Bar No Bar No Bar N oBar 27-26 27-23 186, 500 228, 000 11. 5 35. 0 20-27 22-24 186, 500 228,000 11. 5 35. O 25. 0 24. 0 180, 000 188, 000 l1. 5 35. 7 l9-21 17-16182, 500 190, 000 9. 5 27. 8 21-20 13-12 180, 000 188, 000 11. 5 35. 720. 3 14. 5 161,000 167, 500 13. 5 43. 1 3836 22-22 157, 000 168, 00013. 5 4l. 6 39-39 22-23 159, 000 167, 750 13. 5 42. 4 38. 0 22. 3 109,000 126, 500 19. 0 56. 0 64-67 (5460 110, 000 126, 500 2l. 5 57. 5 66-6458-60 109, 500 126, 500 20. 3 56. 8 65. 8 60. 5

The effect of the tempering temperatures on the physical properties ofthe novel steel alloy is graphically depicted in Figure 9, wherein itwill be seen that tempering ternperatures below 700 F. resulted inspecimens having a Brinell hardness of 400 or more and having Charpyvalues of 20 or more foot pounds at room temperature and 15 or more footpounds at -40 F. Tempering temperatures substantially above 700 F.resulted in inadequate resistance to abrasion because of the low Brinellhardness values shown in Figure 9. At 40 F. a brittle zone resulted fromtempering temperatures above 700 F. and below 900 F. The brittle zone atroom temperature was not so pronounced in the case of this heat;however, it is noted that the lowest Charpy values at room tempera-.ture occurred for specimens tempered at temperatures between 600 and750 F. As above noted, tempering .temperatures below 700 F. resulted insatsifactory Charpy values at room temperature and at -40 F. and alsoresulted in satisfactory Brinell hardness of 400 or more.

Specimens cast from this heat and tempered at values between 250 to 500F. were unusually excellent in that Charpy values at room temperatureand at 40 F. were 20 or more foot pounds and Brinell hardness valueswere 430 or higher.

Example No. 5

Three 200 pound induction furnace heats were poured having the followinganalyses:

Serial Heat C Mn Si P S Cr M Ni B No. No.

The deoxidation practice and the additions of rare earth metals andboron, and calcium-manganese-silicon were substantially the same asthose discussed in connection with previous heats.

- teeth indicating ductility Five dipper teeth castings were poured fromthese heats and were normalized by heating to 1750 F. and holding fortwo hours followed by air cooling. The hardening treatment consisted ofheating the teeth to 1650 F. with a one hour hold at this temperature.This was followed by a water quench until the castings were at atemperature of about 200 F. riihe castings were then reheated to thetempering temperature of about 400 F. with a two hour hold, againfollowed by a water quench. Brinell hardness readings were taken on thecope side of each casting with the following results:

Casting, Serial No.: Brinell 25 534 26 534 27 540 28 534 30 534 Thesecastings were utilized in conventional clipper buckets and weresubjected to trial service in the mining of taconite ore, an unusuallysevere type of service in which prior art teeth were worn to a conditionwhich required replacement loadings. The novel steel alloy teeth `didnot require replacement prior to 533 truck loadings and were ultimatelyremoved to prevent wearing on a new, wider tooth holder placed inservice after the novel teeth had been submitted for tests. According toconservative estimates, approximately 100 additional truck loadingswould have been possible if the novel steel alloy teeth had been in usefor the full service life thereof.

After removal of these novel steel alloy teeth, visual examinationthereof indicated no evidence of spalling, cracking, or bending, and aslight amount of metal flow after service of about 300 truck' wasobserved on the edges of both faces and on the edges of the holdersockets on the sides of the novel thereof, even at the high hardnessvalues above described.

Microscopic examination of the teeth after removal from servicedisclosed a hard white layer of untempered martensitic structure createdby heating the surface to its upper critical temperature of about l500F. and subsequent rapid cooling, due to the service co-nditions to whichthe teeth were subjected. Beneath this layer the teeth were formed ofthe low tempered martensitic structure illustrated in Figure 5.

Example N o. 6

having the following composition:

The heat was killed in the furnace by adding ferromanganese in an amountsufficient to bring the manganese content about equal to that statedabove. The following additions were then made in the ladle: ferrosiliconin an amount to increase the silicon content to about .28, then 3 poundsof aluminum per ton of charge, then l pound of high carbonferrotitaniurn per ton of charge, then 11/2 pounds of the abovedescribed rare earth metal mixture per ton of charge, then .0035 percentby weight of boron in the form of Borosil and finally four pounds ofcalcium-manganese-silicon per ton of charge.

The castings were normalized by heating to about 1750 F. with a two hourhold at that temperature followed by air cooling to about roomtemperature. The castings were then hardened by heating them to about1650 F. with a one hour hold at that temperature followed by a fourminute hold in air at room temperature and then a water quench to about15G-200 F. The castings were then immediately placed into a temperingfurnace and heated to about 300 F. with a two hour hold at thattemperature followed by a water quench to room temperature.

These teeth had a service life of about 913 truck loadings as comparedwith the average of 300 truck loadings for prior art teeth. Brinellhardness readings were taken on two of the teeth before and afterremoval from service with the following results:

It will be understood that certain of the following 4claims recitecertain percentages of the rare earth metals; however, it will beunderstood that the exact amount of such metals in the casting cannot beaccurately measured and the amounts stated in the claims refer to theresidue from the treatment of the molten metal with the amounts of rareearth metals recited by the claims. It is also noted that the term ironin the claims includes residual impurities in ordinary amounts, such as,for example, aluminum, titanium, calcium, copper, lead,l tin and others.

We claim:

1. A steel alloy casting composed of: about .20 to .50% C, about .15 to2.5% Mn, labout .1 to 2.00% Si, nil to about .025% P, nil to about .025%S, about .50 to 1.50% Cr, about .05 to .70% Mo, residual to 1.00% Ni,about .0005 to .005% B, about 0.0015 to 0.5%

Ten `steel alloy dipper teeth were cast from `a heat rare earth metals,the balance-iron, said casting having an internal structure produced bynormalizing at 1600 to 1900 F. followed by air cooling, then heating toabout 1500 to 1650" F. followed by a quench, then heating to about 200to less than 600 F. followed by another quench, and said casting beingcharacterized by the properties of a Brinell hardness value of at least444, and a Charpy impact value of at least 12 foot pounds at 40 F.

2. A steel alloy casting composed of: about .2O to .50% C, about .15 to2.5% Mn, about .l to 2.00% Si, nil to about .025% P, nil to about .025%S, about .50 to 1.50% Cr, about .05 to .70% Mo, residual to 1.00% Ni,about .0005 to .005% B, about 0.0015 to 0.5% rare earth metals, yabout.0005 to .02% Ti, the balance iron, said casting having an internalstructure produced by normalizing at 1600 to 1900 F. followed by aircooling, then heating to about 1500 to 1650 F. followed by a quench, andthen heating to about 200 to less than 600 F. followed by anotherquench, and said casting being characterized by the properties of a`Brinell hardness Value of at least 444, and a Charpy impact value of atleast 12 foot pounds at 40 F.

3. A steel alloy casting composed of: about .20 to .50% C, about .15 to2.5% Mn, about .1 to 2.00% Si, nil to about .05% P, nil to about .05% S,nil to about 5.00% of the group consisting of Cr, Mo, and W, nil toabout 4.00% Ni, about .0005 to .005% B, about 0.0015 to 0.5% rare earthmetals, the balance iron, said casting having a Brinell hardness valueof 444 or more and having a Charpy impact value of the order of at least12 foot pounds at 40 F.

4. A steel alloy casting composed of: about .20 to .50% C, about .15 to2.5% Mn, about .1 to 2.00% Si, nil to about .05% P, nil to about .05% S,nil to about 5.00% of the group consisting of Cr, Mo, and W, nil toabout 4.00% Ni, about .0005 to .005% B, about 0.0015 to 0.5% rare earthmetals, `about .0005 to .02% Ti, the balanceimm said casting having aBrinell hardness value of 444 or more and having a Charpy impact valueof the order of at least 12 foot pounds at 40 F.

5. A steel alloy casting composed of: about .20 to .50% C, about 1.35 to1.55% Mn, about .1 to 2.00% Si, nil to abo-ut .020% P, nil to about.020% S, about .52 to .68% Cr, about .47 to .53% Mo, Ni in residualamount, about .0005 to .005% B, about 0.0015 to 0.5% rare earth metals,the balance iron, said casting being characterized by an internalstructure having plainly visible martensitic needles produced by a heattreatment at about 1600-1900 F., then air cooling, then another heattreatment at about l500-1700 F., followed by a quench, and then atempering heat treatment at about 100-400C F. followed by anotherquench, and said casting being characterized by the properties ofBrinell hardness of about 444 or more and a Charpy impact value of theorder of 15 foot pounds or more at 40 F.

6. A steel alloy casting composed of: about .20 to .50% C, about 1.55 to1.75% Mn, about .l to 2.00% Si, nil to about .020% P, nil to about .020%S, about .70 to .90% Cr, about .47 to .53% Mo, Ni in residual amount,about .0005 to .005% B, about 0.0015 to 0.5% rare earth metals, thebalancehom said casting being characterized by an internal structurehaving plainly visible martensitic needles produced by a heat treatmentat about 1600- 1900 F., then air cooling, then another heat treatment atabout 1450-1650" F., followed by a quench, and then a tempering heattreatment at about 20D-600 F., followed by a quench, and said castingbeing characterized by the properties of a Brinell hardness of about 444or more and a Charpy impact value of the order of 12 or more foot poundsat 40 F.

7. A steel alloy casting composed of: about .20 to .50% C, about 1.25 to2.5% Mn, about .1 to 2.00% Si, nil to about .020% P, nil to about .020%S, about .90

ld to 1.10% Cr, about .50 to .65% Mo, about .90 to 1.10% Ni, about .0005to .005% B, abo-ut 0.0015 to 0.5% rare earth metals, the balance -:`ron,said casting having an internal structure produced by a hardening heattreatment at about 1500-1700" F. followed by a quench, and then atempering heat treatment at about 20G-600 F. followed by another quench,and said casting having the properties of a Brinell hardness of about444 or more and a Charpy value of about 15 foot pounds at 40 F.

8. A steel alloy casting composed of: about .20 to .50% C, about .l5 to2.5% Mn', about .1 to 2.00% Si, nil to about .020% P, nil to about .020%S, about .l to 2.5% Cr, about .05 to 2.5% Mo, about 0 to 4.0 Ni, about.0005 to .005% B, about 0.0015 to 0.5 rare earth metals, about .0005 to.02% Ti, the balance-iron, said casting having an internal structureproduced by a normalizing heat treatment atr about 1600-1900` F.,followed by air cooling, then a hardening heat treatment at about14501700 F., and then a tempering treatment at about 20G-600 F. followedby another quench and having the property of a Brinell hardness valuegreater than about 444.

9. A steel alloy casting composed of: about .35 to .50% C, about 1.35 to2.5% Mn, about .1 to 2.00% Si, nil to about .020% P, nil to about .020%S, about .60 to 2.5% Cr, about .45 to 2.5% Mo, about 0 to about 4.0% Ni,about .0005 to .005% B, about `0.0015 to 0.5% rare earth metals, thebalanceimm said casting having an internal structure produced by anormalizing heat treatment at about 1600-1900 F. followed by aircooling, then a hardening heat treatment at about 0-1700" F. followed bya quench, and then a tempering heat treatment at about 20D-600 F.followed by another quench, and said casting having a Brinell hardnessvalue of at least about 500.

10. A steel alloy casting .5% C, about 1.25 to 1.40% nil to about .020%P, nil to about .020%/S, about .70 to 1.05% Cr, about .50 to .65% Mo,about .90 to 1.00% Ni. about .0005 to .005% B, about 0.0015 to 0.5% rareearth metals, the balance iron, said casting having an internalstructure produced by a hardening heat treatment at about 1600l700 F.followed by a quench, and then a tempering heat treatment at abo-utZOU-600 F. followed by another quench, and said casting having a Brinellhardness of at least about 444.

11. A steel alloy casting composed of: about .20 to .5% C, about .15 to2.5% Mn, about .1 to 2.00% Si, nil to about .020% P, nil to about .020%S, about .70 to 1.05% Cr, about .50 to .65% Mo, about .90 to 1.00% Ni,about .0005 to .002% B, about 0.0015 to 0.5% rare earth metals, about.0005 to .02% Ti, the balance-iron, said casting having an internalstructure produced by a hardening heat treatment at about 1600-1700 F.followed by a quench, and then a tempering heat treatment at aboutZOO-600 F. followed by another quench, and said casting having a Brinellhardness of at least about 444.

l2. A steel alloy casting composed of: about .20 to .5% C, about 1.30 to1.60% Mn, about .l to 2.0% Si, nil to about .05% P, nil to about .07% S,about .50 to .70% Cr, about .40 to .60% Mo, Ni. in residual amount,about .0005 to .005% B, about 0.0015 to 0.5% rare earth metals, thebalance-iron, said casting being characterized by an internal structurehaving plainly visible martensitic needles produced by a heat treatmentat about 1500-1700" F., followed by a quench, and then a tempering heattreatment at about 20G-600 F., followed by another quench, and saidcasting being characterized by the properties of a Brinell hardnessvalue of about 444 or more and a Charpy impact value of the order of 15or more foot pounds at 40 F.

13. A steel alloy casting composed of: about .20 to .5% C, about 1.30 to1.60% Mn, about .1 to 2.0% Si, nil to about .05% P, nil to about .07% S,about .50

composed of: about .20 to Mn, about .1 to 2.00% Si,

l5 to .70% Cr, about .40 to .60% Mo, Ni in residual amount, about .0005to .005% B, about 0.0015 to 0.5% rare earth metals, the balance-iron,said casting being characterized by an internal structure having plainlyvisible martensitic needles produced by a heat treatment at aboutl500-l700 F., followed by a quench, and then -a tempering heat treatmentat about 200-600" F., followed by another quench, and said casting beingcharacterized by the properties of a Brinell hardness value of about444+ or more and a Charpy impact value of the order of 20 or more footpounds at -40 F.

14. In a method of treating molten steel in a basic condition, the stepsof rst deoxidizing the steel and reducing soluble nitrogen in the steelto a value not substantially greater than the order of about .008% byadding titanium in an amount of the order of .0005 to .02% and then,irrespective of sequence, adding boron in an amount of the order of.0005 to .005% and rare earth metals in an amount of the order of 0.0015to 0.5%.

15. In a method of producing wear resisting steel, the steps of killinga bath of molten basic steel comprising: about .20 to .50% C, about .15to 2.5% Mn, about 0.1 to 2% Si, nil to about .05% P, nil to about .07%S, nil

16 to about 5.00% of one or more of the group consisting of Cr, Mo, andW, nil to about 4% Ni, the balance-iron, pouring the metal into theladle and while pouring, making the following additions in the orderspecified: ferromanganese and/ or ferrosilicon and about 1 to 5 poundsof aluminum per ton of charge, then adding titanium in an amount ofabout .0005 to .02% of the charge and then, irrespective of sequence,adding boron in an amount of the order of .0005 to .005% of the chargeand rare 10 earth metals in an amount of the order of 0.0015 to 0.5% o-fthe charge.

References Cited in the le of this patent UNITED STATES PATENTS OTHERREFERENCES Transactions, American Society for Metals, vol. 28, page 618.Published in 1940 by the American Society for Metals, Cleveland, Ohio.

1. A STEEL ALLOY CASTING COMPOSED OF: ABOUT 20 TO .50%C, ABOUT .15 TO2.5% MN, ABOUT .1 TO 2.00% SI, NIL TO ABOUT .025% P, NIL TO ABOUT .025%S, ABOUT .50 TO 1.50% CR, ABOUT .05 TO .70% MO, RESIDUAL TO 1.00% NI,ABOUT .0005 TO .005% B, ABOUT 0.0015 TO 0.5% RARE EARTH METALS, THEBALANCE-IRON, SAID CASTING HAVING AN INTERNAL STRUCTURE PRODUCED BYNORMALIZING AT 1600 TO 1900*F. FOLLOWED BY AIR COOLING, THEN HEATING TOABOUT 1500 TO 1650*F. FOLLOWED BY A QUENCH, THEN HEATING TO ABOUT 200 TOLESS THAN 600*F. FOLLOWED BY ANOTHER QUENCH, AND SAID CASTING BEINGCHARACTERIZED BY THE PROPERTIES OF A BRINELL HARDNESS VALUE OF AT LEAST444, AND A CHARPY IMPACT VALUE OF AT LEAST 12 FOOT POUNDS AT -40*F.